Monday, February 23, 2009

802.1q and ISL trunks

Switches can have multiple vlans. When we connect switches together we use 802.1q trunks (or older ISL trunks) to run multiple vlans over one physical link. With either trunking protocol, a tag is added to the ethernet frame with the vlan information. ISL is an older Cisco-proprietary trunking protocol. Newer switches do not even support ISL. Newer switches use the 802.1q vendor-indepentend trunking protocol. Cisco switches also speak the dynamic trunk protocol (DTP) to dynamically negotiate whether to enable a trunk.



Blogger Darrell Root said...

Diagram is at

February 23, 2009 at 6:24 PM  
OpenID nem642 said...

I was curious what program you use for diagrams on a Mac. I think that was OmniGraffle? Also I have never hooks up a console cable with a Mac. Would you use terminal or something else (is there a SSH option).

-Darin Walker

February 23, 2009 at 7:49 PM  
Blogger Darrell Root said...

My most recent diagrams are omnigraffle. I use zterm with a keyspan USA-19QW USB to serial adapter. My first episode from 2006 "scrounging routers and getting console" covers this in detail (although the early episodes were blurry--sorry about that).

February 24, 2009 at 7:34 PM  
Blogger Charles said...


This was a great presentation. I was wondering if you ever thought of capturing the history so that your viewers (pod people ?) could see all the commands that are entered, right now I rewind and the play back.

In any case great stuff.


March 16, 2010 at 8:46 AM  

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